Human existence is subject to threats operating across vast timescales, from decades to billions of years, making the question of human longevity fundamentally an exercise in risk assessment. Answering how long humanity will last requires considering risks rooted in human technological capacity, the long-term stability of the Earth, and the ultimate destiny of the solar system. Scientific and astronomical models offer a structured framework for understanding these temporal limits and the range of possible futures for our species.
Immediate Existential Risks
The most pressing dangers to human civilization have arisen from our own scientific and industrial advancement, threatening catastrophe within the next century. Industrial activity has pushed the Earth’s climate toward tipping points—thresholds that, once crossed, lead to irreversible, self-accelerating changes in the climate system. Scientists estimate that exceeding 1.5°C of global warming could trigger the collapse of the Greenland and West Antarctic ice sheets, and cause the abrupt thaw of boreal permafrost. These changes are effectively permanent on a human timescale, and the decision point is rapidly approaching, potentially by mid-century.
Technological development itself presents a second tier of immediate, self-imposed risks, particularly from unmanaged Artificial Intelligence (AI) and engineered biological threats. Hundreds of AI experts and tech leaders have stated that mitigating the risk of extinction from advanced AI should be a global priority, ranking it alongside pandemics and nuclear conflict. The concern centers on the potential for a superintelligent AI to develop goals misaligned with human well-being, leading to an uncontrollable outcome or loss of human agency.
The rapid advancement of synthetic biology and gene-editing tools also lowers the technical barrier for creating novel, highly virulent pathogens. This threat is amplified by AI, which can be used to design new biochemical weapons. For example, an AI designed for drug discovery was repurposed to generate 40,000 potential toxic molecules, many more deadly than existing chemical warfare agents. The risk comes not only from deliberate misuse by state or non-state actors but also from the accidental release of an engineered pathogen from a research laboratory.
Natural Planetary Limits
Beyond the dangers we create ourselves lie the natural threats that operate on a geological timescale, measured in thousands to millions of years. Among the most frequent are large-scale impact events from Near-Earth Objects (NEOs), including asteroids and comets. An impactor approximately one kilometer in diameter, capable of causing a global catastrophe, is estimated to strike Earth once every 100,000 to 500,000 years. While “planet-killing” objects like the one that ended the age of the dinosaurs are rare (recurrence interval of about 100 million years), the effects of a one-kilometer impact would be sufficient to collapse global civilization.
Supervolcanic eruptions, classified as magnitude 8 on the Volcanic Explosivity Index (VEI), present a comparable and perhaps more frequent hazard. Geological evidence suggests that a super-eruption occurs roughly once every 100,000 to 200,000 years. An event of this scale, like the Toba eruption 74,000 years ago, would inject vast quantities of ash and sulfur dioxide into the stratosphere, causing a prolonged “volcanic winter.” This effect would severely cool global temperatures for years, leading to widespread crop failure, mass starvation, and the collapse of global food supplies.
On a much longer timescale, natural geophysical processes will eventually alter the planet’s habitability. In the distant future, between 1.5 and 4.5 billion years from now, the stabilizing effect of the Moon’s gravity may diminish, causing Earth’s axial tilt to undergo chaotic variations. This shift could lead to extreme climate swings and may render the planet uninhabitable long before the Sun’s final evolution begins. Additionally, the continuous process of plate tectonics will lead to the formation of a new supercontinent in 250 to 350 million years, which would drastically alter ocean currents, weather patterns, and global biodiversity.
The Final Limit of Solar Evolution
The final limit for human survival on Earth is set by the life cycle of the Sun, which will eventually render the planet uninhabitable. The Sun is currently halfway through its stable main-sequence phase, but its luminosity is steadily increasing as it converts hydrogen into helium in its core. In approximately 1.1 billion years, the Sun’s radiation output will be about 10% higher than today, a change sufficient to trigger a runaway greenhouse effect on Earth.
This increased solar flux will cause the oceans to evaporate completely, filling the atmosphere with water vapor and creating a surface temperature too high for liquid water or complex life. The extinction of all complex life will occur long before this point, likely in the next 800 million years, as the rising heat disrupts the carbon cycle and causes plants to die off. The final phase of solar evolution will occur in about 5.4 billion years, when the Sun exhausts the hydrogen in its core and expands into a red giant. This expansion will increase the Sun’s radius dramatically, potentially engulfing the orbits of Mercury, Venus, and possibly Earth, resulting in the planet’s destruction.
Strategies for Prolonging Survival
The only way for humanity to bypass the three categories of existential limits—self-imposed, planetary, and solar—is to become a multi-planetary and, eventually, an interstellar species. The first step involves establishing self-sustaining off-world habitats, with the Moon and Mars being the most immediate targets for colonization within the coming decades. These habitats must be closed-loop, artificial ecosystems capable of recycling all resources, including water, air, and waste. This requires mastering in-situ resource utilization, such as extracting oxygen from Martian soil or lunar regolith, to ensure independence and resilience against a single planetary catastrophe.
To escape the ultimate fate of the solar system, humanity will need to achieve interstellar travel, a challenge currently constrained by the vast distances between stars and the limitations of conventional chemical propulsion. The concept of “generational ships,” where multiple generations live and die aboard a vessel traveling at sub-light speeds, represents one slow but feasible approach. More advanced concepts currently under research include fusion-driven rockets and directed-energy propulsion, such as the laser-pushed light sail.
While technologies like antimatter drives and warp drives remain purely theoretical, beamed energy propulsion is based on known physics. It could theoretically achieve a fraction of the speed of light, potentially reaching the nearest star system in decades. Becoming a true interstellar species would provide a final escape from the Sun’s demise and serve as the best insurance against any unforeseen catastrophe, ensuring the indefinite continuation of the human lineage across the galaxy.